For awhile, Google's been using their own goo.gl shortener to compress long links, but as of today they'll be using a different shortener, g.co. However, the goal behind g.co is not to provide another URL shortener for you to create short links. Instead, it's a service that only Google can use to shorten links to their own pages—that way, when you see a g.co link, you know that it's coming from a trusted source and you can click on it. For your own links, you can still use Goo.gl, but just know that when you see a g.co link around the internet, it's coming straight from Google and is safe to click on. [Official Google Blog]